MULTISHOT ABLATION OF POLYMER AND METAL-FILMS AT 248-NM

The photoacoustic mirage effect technique was utilized to investigate excimer laser ablation of thin polymer (photoresist) and metal films. Layered systems, consisting of a photoresist-metal-SiO2 structure, were ablated by KrF (lambda = 248 nm) laser radiation at fluences up to 2 J/cm2. For the photoresist layer a linear dependence of the deflection amplitude on the etch rate was found in the low fluence regime (less-than-or-equal-to 0.7 J/cm2). Significant changes in the deflection signal occurred when the ablation passed the interface between subsequent layers. This effect can be used to distinguish between different layers. Therefore, shock wave monitoring in principle offers the possibility for an in situ control of laser thin film processing. Selective ablation of metal films from the SiO2 layer is limited to fluences below 2 J/cm2.